Can pho be served ice cold?

A (somewhat south) Vietnamese not currently in Vietnam chiming in ^^ :

Apart from some exceptions (like cà phê s?a ?á) I have the impression that there are no traditional ice-cold Vietnamese dishes whatsoever (I'd even dare to say that almost all desserts are eaten warm or at least at "room temperature" at 36°C / 96°F). Maybe it's just due to the non-availability of ice and constant power outrages that lead to cozy 20°C / 68°F in the freezer. What I've also observed is my Vietnamese relatives in Vietnam always want to have their tender herbs / lettuce / mung bean sprouts blanched and served immediately. The reasons are omnipresent nasty pathogens.

(Don't ask me how they eat their bún ch? or bánh xèo with lettuce without getting belly-ache. Perhaps it's all about mitigating risk but not completely avoiding it at all costs.)

To answer the question: Probably no. At least not traditional ph?.

You could do it, but you would need to clarify the broth or it would have a somewhat impalpable fatty chew to it. And by clarifying a finished broth, you would alter the taste a bit more than discretely.

That does not make it impossible, you will just need to change the order of your stock(s). Start with any fatty components, clarify the broth, add the non-fatty stuff, simmer as usual, cool then skim any fat remaining.

Otherwise you are likely to get a greasy-ish texture, which you probably don't want in a cold soup. You can also just skim thoroughly before serving but if the stock has more than a small bit of fat in it, well...

I'm not sure how authentic it is, but I was able to find an often repeated dish referred to as Cold Soba Noodles with Vietnamese Pork that is in a way more like mul-naengmyeon than Pho because it's made with buckwheat noodles.

Here's the list of ingredients from one example recipe of the Vietnamese dish from Cooking Light on My Recipes:

3 tablespoons chopped green onions, divided

2 tablespoons dark sesame oil, divided

4 teaspoons fish sauce, divided

1 tablespoon reduced-sodium tamari

2 teaspoons brown sugar

1/4 teaspoon freshly ground black pepper

1/2 pound boneless pork cutlets, trimmed and cut into 1/2-inch-thick strips

8 ounces uncooked organic soba noodles

2 tablespoons rice wine vinegar

1 teaspoon chile paste with garlic (such as sambal oelek)

3 cups chopped napa (Chinese) cabbage

1/2 cup finely chopped red bell pepper

Cooking spray

Here's the picture from that recipe:

For comparison, here's the list of ingredients from a recipe for mul-naengmyeon that I'm happy to plug because the author is a favorite vlogger of mine, Maangchi's mul-naengmyeon:

10 ounces (280 grams) dried naengmyeon (buckwheat) noodles

2 packets of liquid or powdered concentrated broth that comes with the package of naengmyeon noodles

2 packets of mustard oil that comes with the package of naengmyeon noodles.

½ English cucumber, cut into thin strips

1 Korean pear (or 2 bosc pears)

½ teaspoon salt

1½ teaspoon sugar

1 tablespoon white or apple cider vinegar

1 hard-boiled egg, cut in halves

2 tablespoons toasted sesame seeds, ground

ice cubes

Here's her video of that recipe

And the thumbnail from that video: